Fuel Injector Control System and Method to Compensate for Injector Opening Delay

ABSTRACT

A fuel injector control system including a fuel injector, a sensing device configured to provide a transition signal indicative of a fuel injector transition from the closed-state to the open-state, and a controller configured to determine an injector control signal based on the transition signal. The injector control signal closing time can be adjusted base on the transition signal and so compensate for injector opening delay due to, for example, a stuck closed fuel injector, cold temperatures, or low injector drive voltages.

TECHNICAL FIELD OF INVENTION

The invention generally relates to fuel injector control systems andmethods, and more particularly relates to a system and method fordetecting a transition time when a fuel injector transitions from aclosed-state to an open-state.

BACKGROUND OF INVENTION

Fuel injectors in internal combustion engines are generally operated byalternately switching the fuel injector between a closed-state where nofuel is dispensed by the fuel injector, and an open-state where fuel isdispensed by the fuel injector. It has been observed that some fuelinjectors may stick and remain closed for an indefinite period of timeafter a signal to open the fuel injector has been applied to the fuelinjector. This problem is particularly evident if it is the first timethe injector is being opened after being in the closed-state for anextended period of time, for example, when a vehicle is parkedover-night with the engine off. It has been observed that certaininjector designs, such as compressed natural gas (CNG) injectors thatuse an elastomer to better seal a pintle/seat interface, are moresusceptible to sticking than metal-to-metal type seals. Also, it hasbeen observed that some fuel injectors are more susceptible to stickingif the ambient temperatures are relatively low, for example less than−20 degrees Celsius. If a fuel injector does not transition from theclosed-state to the open-state predictably, the amount of fuel dispensedby the injector may be uncertain.

SUMMARY OF THE INVENTION

In accordance with one embodiment of this invention, a fuel injectorcontrol system is provided. The system includes a fuel injector, asensing device and a controller. The fuel injector is configured torespond to a control signal for operating the fuel injector to aclosed-state and an open-state. The sensing device is configured toprovide a transition signal indicative of a fuel injector transitionfrom the closed-state to the open-state. The controller is configured todetermine the control signal based on the transition signal.

In another embodiment of the present invention, a controller forcontrolling a fuel injector is provided. The controller includes acontrol signal output, a sensor signal input, and a processor. Thecontrol signal output is configured to output a control signal foroperating the fuel injector to a closed-state and an open-state. Thesensor signal input is configured to receive a transition signalindicative of a fuel injector transition from the closed-state to theopen-state. The processor is configured to determine the control signalbased on the transition signal.

In yet another embodiment of the present invention, a method ofcontrolling a fuel injector is provided. The method includes the step ofoutputting a control signal to operate the fuel injector to aclosed-state and an open-state. The method also includes the step ofreceiving a transition signal indicative of a fuel injector transitionfrom the closed-state to the open-state. The method further includes thestep of adapting the control signal based on the transition signal.

Further features and advantages of the invention will appear moreclearly on a reading of the following detailed description of thepreferred embodiment of the invention, which is given by way ofnon-limiting example only and with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a fuel injector system in accordancewith one embodiment;

FIG. 2 is a graph of signals present in FIG. 1 in accordance with oneembodiment; and

FIG. 3 is flowchart of a method of operating the system of FIG. 1 inaccordance with one embodiment.

DETAILED DESCRIPTION OF INVENTION

In accordance with an embodiment of a fuel injector control system, FIG.1 illustrates a system 10 that includes a drive circuit 12 and acontroller 14 electrically coupled to a fuel injector 20. The fuelinjector is generally configured to operate in response to a controlsignal 18 from the drive circuit 12 for operating the fuel injector to aclosed-state where no fuel is dispensed by the fuel injector 20, and anopen-state where fuel is dispensed by the fuel injector 20. In thisnon-limiting example, the fuel injector 20 illustrated is anelectromagnetic type that operates a valve or pintle/seat arrangement 22between an open-state corresponding to an open position as illustrated,and a closed-state corresponding to a closed position as illustrated.The open position allows fuel to be dispensed by the fuel injector 20,and the closed position blocks fuel from being dispensed by the fuelinjector 20. While only one fuel injector 20 is illustrated, theteachings herein may be applied to systems having multiple fuelinjectors, as will be described in more detail below.

FIG. 1 further illustrates a non-limiting example of a drive circuit 12suitable for operating the fuel injector 20. The drive circuit isillustrated as being separate from the controller 14, but it will beappreciated that these and other features illustrated in FIG. 1 could beintegrated into a single unit such as within the controller 14. Thedrive circuit 12 may include a voltage source VS to provide a suitablevoltage potential to operate the fuel injector 20, for example 14 Volts.The voltage source VS may be a battery as suggested in the illustration.The battery may be rechargeable, such as a lead acid battery, and thebattery may be connected to a vehicle electrical system (not shown)configured to recharge the battery. The drive circuit may also include aswitch SW operable connect or disconnect the voltage source VS and thefuel injector 20. The switch SW is preferably a solid state device suchas a transistor (e.g.—MOSFET, IGBT), but could be a relay or like. Theswitch SW may be operated by the control signal 18 from the controller14. The control signal 18 may be a steady signal that holds the switchSW in the closed state for a period of time to influence a desiredinjection time of the fuel injector 20, or may be apulse-width-modulated (PWM) signal having a variable duty cycle.

It has been observed that some fuel injectors do not consistentlytransition from the closed-state to the open-state. For example, somefuel injectors may stick in the closed-state for a period of time beforetransitioning to the open-state, and so the amount of fuel dispensed bythe fuel injector may be reduced as a result of this transition delay.Fuel injectors equipped with an elastomer seal (not shown) as part ofpintle-seat arrangement 22 have been observed to be more susceptible totransition delay than fuel injectors that do not have elastomer seals.Fuel injectors for dispensing gaseous fuel such as compressed naturalgas (CNG) are sometimes equipped with elastomer seals to reduce the riskof fuel leaking while in the closed-state. It has also been observedthat some fuel injectors may be more prone to exhibiting the transitiondelay when ambient temperatures are relatively low, less than −20degrees Celsius for example. It has also been observed that some fuelinjectors are more prone to exhibiting transition delay if the voltageapplied to the fuel injector is lower than normal, such as less than 10Volts which may occur during engine cranking when starting an engine.

The problem of transition delay causing inaccurate fuel metering by thefuel injector may be solved by the system 10 being equipped with asensing device 24 configured to provide a transition signal indicativeof the fuel injector 20 transitioning from the closed-state to theopen-state. If the transition signal is provided, then the controller 14may be configured to determine the control signal 18 based on thetransition signal. For example, if the fuel injector 20 exhibitstransition delay while transitioning from the closed-state to theopen-state, the control signal 18 may be adjusted to hold the injectorin the open-state longer so the proper amount of fuel is dispensed bythe fuel injector 20. As another example, if no transition signal isdetected because the injector is stuck in the closed-state, the controlsignal 18 is cycled, optionally more rapidly than the normal engineinjector firing frequency, in order to overcome any stiction between thepintle-seat arrangement 22.

Some systems may be configured to dispense a secondary fuel, for examplea liquid fuel as an alternative to a gaseous fuel, and so be equippedwith a secondary fuel injector (not shown) in addition to the fuelinjector 20. Then if no transition signal is detected, or if conditionsare such that the secondary fuel is preferable (e.g. low ambienttemperature), controller 14 may be configured to dispense the secondaryfuel until conditions change (e.g. the engine warms up), or a transitionsignal from the fuel injector 20 is observed a the result of ‘testing’the fuel injector 20 until a transition signal is detected. In addition,if a pre-determined amount of time elapses, or a pre-determined numberof attempts to operate the fuel injector 20 are executed without atransition signal being detected, controller 14 may be configured notifythe vehicle operator that it has detected a fault in the fueling system,by, for example, illuminating a service-engine indicator. Furthermore,controller 14 may be configured to provide diagnostic information via adiagnostic device (not shown) when prompted by a service technician.

In one embodiment, the sensing device 24 may be a current sensor 26arranged to measure injector current I, for example a 0.1 Ohm resistorR1 arranged in series with an injector coil 16 of the fuel injector 20.Alternative ways of measuring current are well known, such as Halleffect sensors. The current sensor 26 is generally configured to outputa current signal 28 to the controller 14, for example to ananalog-to-digital convertor ADC within the controller 14. As will beexplained in more detail below, the transition signal may be based on aninjector current I as indicated by the current signal 28. In anotherembodiment the sensing device 24 may be a pressure sensor 30 outputtinga pressure signal 32, and as will be explained below the transitionsignal may be based on a fuel pressure P indicated by the pressuresignal 32. In yet another embodiment the sensing device 24 may includeboth the current sensor 26 and the pressure sensor 30, and thetransition signal may be based on either or both the current signal 28and the pressure signal 32.

FIG. 2 illustrates a non-limiting graphical depiction of a controlsignal 18 output by the controller 14, and a typical current signal 28and pressure signal 32 occurring in response to the control signal 18.The timing of the control signal 18 transition from OFF to ON is anon-limiting example for the purposes of explanation. Three exampletransition signals T1, T2 and T3 are illustrated. The three transitionsignals are illustrated as occurring at different moments in time onlyfor the purposes of explanation, and may under certain circumstancesoccur at the same moment in time, or in a different relative order.

A first transition time T1 is illustrated as corresponding to aninflection in the current signal 28. The inflection may be detected bydetermining a current signal slope of the current signal 28, anddetermining that the time that the first transition signal T1 occurscorresponds to the moment when the current signal slope is less than acurrent slope threshold, for example less than zero (i.e.—a negativeslope). Alternatively, the first transition signal T1 may be determinedto correspond to the moment when the current signal slope changes to apositive slope following the momentary negative slope illustrated. Whilenot subscribing to any particular theory, it is believed that themovement of the valve surrounded by the injector coil 16 induces avoltage that opposes the supply voltage VS and so causes a momentarydecrease in the injector current I.

When the fuel injector 20 transitions from the closed-state to theopen-state, a corresponding decrease in fuel pressure P of fuel suppliedto the fuel injector 20 has been observed. A second transition time T2is illustrated as corresponding to a point in time when the pressuresignal 32 exhibits a pressure signal slope 33 less than a pressure slopethreshold 34. Alternatively, the second transition time T2 may be whenthe pressure signal slope 33 is less than the pressure slope threshold34 for a predetermined period of time. By requiring that the pressuresignal slope remain less than the pressure slope threshold 34 for aperiod of time, transient noise in the pressure signal or pressuresignal slope can be filtered or ignored.

Alternatively, instead of examining the pressure signal slope, thecontroller 14 simply compare the value of the pressure signal 32 to apressure value threshold 36, and may indicate that at third transitionsignal T3 has occurred when the pressure signal value is less than apressure value threshold 36. Also, the controller 14 may indicate that atransition signal has occurred when both the pressure signal slope 33 isless than a pressure slope threshold 34 and the pressure signal value isless than the pressure value threshold 36.

In another embodiment the system may have both the current sensor 26 andthe pressure sensor 30. For this case the transition signal may be basedon both injector current I and fuel pressure P. As such, for thisexample, the system 10 may be equipped with a sensing device 24 thatoutputs a current signal 28 characterized as having a current signalslope, and outputs a pressure signal 32 characterized as having apressure signal slope and a pressure signal value. Then a transitionsignal may be indicated by any combination of the current signal slopebeing less than a current slope threshold, or the current signal slopebecoming positive following a period of negative slope (T1), and/or thepressure signal slope 33 being less than a pressure slope threshold 34(T2), and/or the pressure signal value being less than a pressure valuethreshold 36 (T3).

The controller 14 may include a processor such as a microprocessor orother control circuitry as should be evident to those in the art. Thecontroller 14 may include memory, including non-volatile memory, such aselectrically erasable programmable read-only memory (EEPROM) for storingone or more routines, thresholds and captured data. The one or moreroutines may be executed by the processor to perform steps fordetermining if signals received by the controller 14 for controlling thefuel injector 20 as described herein. The controller 14 may also includea control signal output configured to output the control signal 18 foroperating the fuel injector to a closed-state and an open-state. Thecontroller 14 may also include a sensor signal input such as theanalog-to-digital convertor ADC illustrated that is configured toreceive a transition signal indicative of a fuel injector transitionfrom the closed-state to the open-state. The processor may also beconfigured to determine or adapt the control signal 18 based on thetransition signal T1, T2, and/or T3.

FIG. 3 illustrates a method 300 of controlling a fuel injector. Step310, OUTPUT CONTROL SIGNAL, may include outputting a control signal 18by the controller 14 to operate the fuel injector 20 from theclosed-state to the open-state.

Step 320, RECEIVE CURRENT SIGNAL, may include receiving a firsttransition signal T1 indicative of a fuel injector transition from theclosed-state to the open-state based on injector current I as indicatedby current signal 28

Step 330, DETERMINE CURRENT SLOPE, may include determining when thefirst transition signal T1 occurs by determining when a slope of acurrent signal 28 has a current slope value less than a current slopethreshold, for example zero. Step 330 may also include determining thatthe current slope has changed by an amount greater than a current slopechange threshold, for example when the current slope changes fromnegative to positive.

Step 340, RECEIVE PRESSURE SIGNAL, may include receiving a secondtransition signal T2 and or a third transition signal T3 indicative of afuel injector transition from the closed-state to the open-state basedon fuel pressure P as indicated by pressure signal 32.

Step 350, DETERMINE PRESSURE SLOPE, may include determining when thesecond transition signal T2 occurs based on when a slope of the pressuresignal 32 has a slope value 33 less than a slope threshold 34.

Step 360, DETERMINE TIME OF TRANSITION SIGNAL, may include determine thetime when any one of the transition signals T1, T2, or T3 occurs, or thetime when all of the transition signals T1, T2, and T3 have occurred.

Step 370, ADAPT CONTROL SIGNAL, may include adapting the control signal18 based on the transition signal T1, T2 and/or T3. Adapting the controlsignal 18 may include extending the ON time of the control signal inresponse to detecting that an opening delay or transition delay of thefuel injector 20 has occurred.

Accordingly, a fuel injector control system 10, a controller 14 for thefuel injector control system 10 and a method 300 of controlling a fuelinjector 20 are provided. By sensing a time when the fuel injector 20actually transitions from the closed-state to the open-state, thecontrol signal 18 can be compensated or adapted so the desired amount offuel is dispensed by the fuel injector 20 even if the transition time isabnormally delayed. The slope of the current signal 28 may be used todetect the transition moment because of the observed inflection in thecurrent signal 28 corresponding to the fuel injector opening. The fuelpressure signal 32 may also be used to estimate when the fuel injector20 actually opens. While some fuel injector designs and/or operatingconditions have opening characteristics that are repeatable enough thatdetermining a transition time based on a transition signal (T1, T2, T3)is not necessary, certain injectors and certain operating conditions maywarrant determining a transition time so fuel is accurately dispensed.

While this invention has been described in terms of the preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

1. A fuel injector control system, said system comprising: a fuelinjector configured to respond to a control signal for operating thefuel injector to a closed-state and an open-state; a sensing deviceconfigured to provide a transition signal indicative of a fuel injectortransition from the closed-state to the open-state; and a controllerconfigured to determine the control signal based on the transitionsignal.
 2. The system in accordance with claim 1, wherein the fuelinjector includes a pintle-seat arrangement that includes an elastomerseal.
 3. The system in accordance with claim 1, wherein the fueldispensed by the fuel injector is gaseous.
 4. The system in accordancewith claim 1, wherein the transition signal is based on injectorcurrent.
 5. The system in accordance with claim 4, wherein the sensingdevice outputs a current signal characterized as having a current signalslope, wherein transition signal is indicated when the current signalslope is less than a current slope threshold.
 6. The system inaccordance with claim 1, wherein the transition signal is based on fuelpressure.
 7. The system in accordance with claim 6, wherein the sensingdevice outputs a pressure signal characterized as having a pressuresignal slope, wherein the transition signal is indicated when thepressure signal slope is less than a pressure slope threshold.
 8. Thesystem in accordance with claim 6, wherein the sensing device outputs apressure signal characterized as having a pressure signal value, whereinthe transition signal is indicated when the pressure signal value isless than a pressure value threshold.
 9. The system in accordance withclaim 1, wherein the transition signal is based on injector current andfuel pressure.
 10. The system in accordance with claim 9, wherein thesensing device outputs a current signal characterized as having acurrent signal slope and outputs a pressure signal characterized ashaving a pressure signal slope and a pressure signal value, wherein thetransition signal is indicated when the current signal slope is lessthan a current slope threshold, the pressure signal slope is less than apressure slope threshold, and the pressure signal value is less than apressure value threshold.
 11. The system in accordance with claim 1,wherein the controller determines the control signal based on thetransition signal if an ambient temperature is less than an ambienttemperature threshold.
 12. A controller for controlling a fuel injector,said controller comprising: a control signal output configured to outputa control signal for operating the fuel injector to a closed-state andan open-state; a sensor signal input configured to receive a transitionsignal indicative of a fuel injector transition from the closed-state tothe open-state; and a processor configured to determine the controlsignal based on the transition signal.
 13. A method of controlling afuel injector, said method comprising the steps of: outputting a controlsignal to operate the fuel injector to a closed-state and an open-state;receiving a transition signal indicative of a fuel injector transitionfrom the closed-state to the open-state; and adapting the control signalbased on the transition signal.
 14. The method in accordance with claim13, wherein the method includes the step of determining when thetransition signal occurs.
 15. The method in accordance with claim 14,wherein the step of determining when the transition signal occursincludes determining a slope of a sensor signal.
 16. The method inaccordance with claim 15, wherein the step of determining when thetransition signal occurs includes determining that the slope has a slopevalue greater than a slope threshold.
 17. The method in accordance withclaim 15, wherein the step of determining when the transition signaloccurs includes determining that the slope has changed by an amountgreater than a slope change threshold.
 18. The method in accordance withclaim 14, wherein the step of determining when the transition signaloccurs includes determining a value of a sensor signal and that thesensor signal has a value greater than a threshold value.
 19. The methodin accordance with claim 14, wherein the step of determining when thetransition signal occurs includes measuring fuel injector current. 20.The method in accordance with claim 14, wherein the step of determiningwhen the transition signal occurs includes measuring fuel pressure.